PROJECT SUMMARY Significant progress has been made in the development and refinement of diagnostic measures for autism spectrum disorder (ASD). However, these measures do not capture fine-grained changes in social- communication that occur over time or in response to treatment. Existing measures of social-communication are also strongly influenced by developmental level, thus making scores difficult to compare across children with ASD or other neurodevelopmental disorders (NDDs) who differ in age and ability. Given the wide range of cognitive abilities observed in children with ASD, and recent advances in the identification of multiple genetic syndromes associated with ASD and varying levels of intellectual disability, there is increasing need for measures that assess social-communication abilities while accounting for development (both age and IQ). The lack of instruments to quantify social-communication ability relative to developmental level and sensitive to incremental change poses a major obstacle for treatment studies in particular. The specific objective of the proposed research is to create and validate a measure of social- communication ability that can be used to describe baseline levels of ability and subsequent stability or change in children with ASD and other NDDs. Scores will be standardized within specific developmental cells (age x IQ), thus pre-emptively managing the substantial measurement challenges caused by variability in how behaviors manifest in children of different ages and abilities. The new measure will be specifically designed to be sensitive to gains associated with the continuation of development, as well as to incremental treatment- related improvements in skills that may be obscured by broad measures of impairment (e.g., diagnostic tools). Phase 1 of the project will involve analyses of existing ASD symptom measures from more than 10,000 assessments of children with ASD (n=7,838), non-ASD NDD (n=1,595), or typical development (TD) (n=636) in order to identify constructs that are most relevant to social-communication ability within developmental cells, and that are maximally responsive to developmental changes. Items will be written from the identified constructs and designed for a computer-adaptive testing format (CAT). This will allow for complex skip patterns that tailor content within particular developmental windows, and will facilitate web-based distribution of the tool. During Phase 2, the candidate item pool will be administered via computer- or tablet-based administration to parents of children with ASD or other NDDs across multiple clinical sites (projected ASD n=930, projected non- ASD NDD n=670), and via the internet to parents of non-clinically referred children (projected n=400), in order to evaluate the dimensionality of the proposed new measure (Phase 2a), and cross-validate and calibrate the items that perform as expected (Phase 2b). In Phase 3, the final item bank will be field tested via the CAT prototype with 100 clinical or research referrals with ASD or non-ASD NDD. The resulting measure will provide information about a child's social-communication abilities relative to an age- and IQ-matched reference group.